1. Field of the Invention
The present invention relates to a method and an apparatus for connecting buses of a computer system, and more particularly to a method and an apparatus for connecting buses with different clock frequencies.
2. Description of the Related Art
In computer systems, buses are very important devices. With buses, the essential components of computer systems, such as central processing units (CPU), memories and peripheral devices, are able to communicate with each other. Devices connected to buses include master devices and slave devices. Master devices, such as CPU, transmit requests. Slave devices, like peripheral devices, execute requests. The function of buses is to transfer requests and responses of requests.
Buses are shared by all devices so they tend to become the bottleneck during data transmission. Only one master can use the bus at one time. The other masters can only transmit requests after the execution of the previous request is completed. Accordingly, one solution is to put multiple buses in the system such that requests transmitted from masters connected to different buses can be simultaneously and individually executed on different buses. For example, the advanced high-performance system bus (AHB) proposed by ARM Corp. is one such solution.
These buses must be able to communicate to each other, which is made possible by a transfer matrix in the multi-layer AHB. A transfer matrix is a conversion interface among buses, in which a master of a bus can use a slave of another bus without affecting the operation of other buses.
The specifications of the multi-layer AHB, however, do not mention the issue about buses with different clock frequencies. Therefore, the question of how the transfer matrix connects buses with different clock frequencies is still not answered.
U.S. Patent Publication No. 20020162043 provides a structure for connecting an AHB and an advanced peripheral bus (APB) in the advanced microcontroller bus architecture (AMBA). In the structure, a master of the high-speed AHB can use a slave of the low-speed APB. The structure, however, cannot handle the situation where the slave is connected to high-speed buses. In addition, the structure can only be used in a two-bus system, but not in a system with more than two buses.
Accordingly, a more flexible solution is required to connect at least three buses with different clock frequencies and overcome the disadvantages of the prior art.